Many hormones, neurotransmitters, and growth factors exert their effects by stimulating turnover of inositol phospholipids. Phosphodiesteratic cleavage of phospharidylinositol-4,5- bisphosphare (PIP2) generates two intracellular second messengers, inositol-1,4,5-trisphosphare and diacylglycerol. The mechanism and regulation of this transmembrane signaling pathway are currently the subjects of intense investigation. Less attention is being given to the possibility that enzymes that control the PIP2 pool size may be regulate directly or indirectly by elements of the pathway. This project addresses this question, focusing on phosphatidylinositol (PI) kinase, a membrane-bound enzyme which catalyzes the first step in polyphosphoinositide synthesis. Recent advances in understanding of protein solubilization by detergents will aid purification of PI kinase from rat liver, and antibodies will be raise to the purified enzyme. Its kinetic characteristics will be determined under conditions where the physical properties of the enzyme and lipid substrate are controlled. Using isolated hepatocytes, regulation of PI kinase will be investigated under conditions where the vasopressin and delta l-adrenergic receptor systems are activated, desensitized, or up-regulated. Potential regulation by phosphorylation, proteolysis, diffusible regulators, and amount and subcellular distribution of both PI and enzyme, will be examined. Receptors which stimulate phosphoinositide turnover play roles in immune responses and regulation, release of insulin and several pituitary hormones, growth control, and malignant transformation, to name a few. These studies will help better to define biochemical events related to mechanisms of receptor action and regulation, and therefore will almost certainly have eventual application to the understanding and treatment of human diseases.